A machine such as, for example, an off-highway truck, may include one or more sources of power. Power sources may include engines, batteries, and any other suitable energy generating or energy storage devices. The machine may also include powered devices that may run using power generated or otherwise supplied by the power source. When operating such a machine, it is useful to prevent stalling of the power source that operates the machine.
For example, during operation of the machine, multiple powered devices may request power from the power sources. At times, power requests may conflict because the power sources may not be capable of fulfilling each and every power request. If power requested by the powered devices exceeds the available power from the power source, some or all of the powered devices may not receive sufficient power, and/or the power source may fail or stall. Power source failures may result in machine downtime and decreased efficiency.
Engine braking may contribute to stalling of such machines. For example, during cold engine operation when the lubricating oil is cold and thick, engine braking tends to stall the engine because engines generally need a richer fuel mixture in order to maintain idle speed while warming up. Also, during slow speeds, and in particular during a panic stop, where the engine speed is decreasing rapidly, turning off engine braking at the traditional engine speeds of between 800-1000 rpm does not give the engine enough time to recover and may result in engine stalling. One approach has been to disable engine braking just prior to the traditional engine speeds. However, this approach prevents an operator from performing slow-speed engine braking, which may be necessary in situations where a machine such as a gravel truck enters a pit mine.
A system to prevent engine stalling is described in U.S. Pat. No. 5,146,891 (the '891 patent) to Nakazawa et al. The '891 patent discloses a system and method for controlling an operation of an internal combustion engine of a vehicle having an automatic transmission. The '891 patent varies at least one of predetermined fuel supply recovery engine revolution speed or predetermined fuel supply cut-off engine revolution speed during engine deceleration and in accordance with a state of operation of the automatic transmission. The '891 patent detects the engagement of the engine brake controlling clutch and can either delay or quicken the timing of both the fuel supply cut-off and fuel recovery, thereby preventing engine stalls.
Although the system of the '891 patent may prevent engine stalls, it does not compensate for either cold engine operating mode or slow speed operating mode. For example, engine braking tends to stall engines during cold engine operation and in situations where the engine speed is decreasing rapidly. Thus, the system of the '891 patent may not sufficiently prevent engine stalls in all engine operating situations.
The disclosed power source braking system is directed to overcoming one or more of the problems set forth above.